WASHINGTON — President Obama is preparing to deliver his fourth State of the Union address on Tuesday at — or close to — the height of his political power. He has been reelected convincingly, won legislative showdowns with Republicans on debt and spending issues, and is basking in some of his highest approval ratings in years.

Of course, modern political history has shown that political momentum can disappear — or at least erode — rapidly. That’s especially true for a second-term president, who probably has until the midterm election — 2014 in Obama’s case — to either use or lose his political power.

So, how can Obama use the speech to keep on his current political roll? Here are three ideas:

It’s the deficit, stupid. A look back at Obama’s first three State of the Union speeches, plus the address to a joint session of Congress in 2009, suggests a similar thematic pattern: He starts with the economy, moves to education and then, in the middle section of the speech, addresses the deficit. (The exception was in 2011, when Obama began his speech with a riff on partisanship.) In 2012, Obama spent just five minutes on the debt— less time than he spent on partisanship (5½ minutes) or foreign policy (six minutes).

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He should flip that script in this State of the Union and spend the bulk of his time talking about the deficit. Here’s why: In January 2009 polling by Pew Research Center, 53 percent of respondents said reducing the deficit was a “top priority.” In January 2013, that number soared to 72 percent, by far the biggest increase of any issue over that time. (By contrast, 85 percent said strengthening the economy was a top priority in 2009, while 86 percent said so at the start of this year.)

The debt is the issue of the day, and one that, if Obama is beginning to eye his legacy as president, could go a long way toward shaping how history remembers him. Make this speech a deficit speech.

Pressure Republicans. Much of Obama’s success since the November election has been born of a willingness to take advantage of the fact that congressional Republicans are not only deeply unpopular with the public at large but internally divided over the future of the party — and without a clear leader to guide them. (The choice of Marco Rubio as the Republican responder to Obama’s State of the Union address suggests the GOP establishment would like the Florida senator to be that leader.)

Polling tells the story. While Obama’s job approval rating was at 55 percent in a January Washington Post-ABC News survey, just 24 percent of respondents approved of the job performance of Republicans in Congress. And two-thirds of the sample (67 percent) said Republicans were doing too little to compromise with the president on major issues.

Given those numbers, there’s every reason for Obama to continue the aggressive approach he has taken in his dealings with Republicans since winning a second term in November. Act, oratorically speaking, and force Republicans to react.

Pick a pet issue — just one. A look at the Pew priorities polling conducted last month is a telling indicator of the public’s priorities. Of 21 issues tested, global warming ranked dead last among those priorities, while strengthening gun laws came in 18th and illegal immigration 17th.

And yet, that trio of issues — along with the economy— has been at the forefront of political and policy discussions in Washington over the past few months. (Circumstances obviously matter here; the shootings in Newtown, Conn., thrust gun laws into a spotlight they would never have had if that tragedy had not happened.)

What that discrepancy should tell Obama is that he needs to tread carefully on those issues in his State of the Union speech, and beyond. While most people would like to see all of them addressed, none are even close to the priority of fixing the economy or reducing the debt. And so, Obama would be smart to pick one — guns seems by far the most likely — and spend real time on it in the speech, with only a passing reference or two to the others.